The present invention relates to an apparatus for valve actuation in a multi-cylinder internal combustion engine, and, more particularly, to a valve actuator in an engine having, per cylinder, an actuation lever driving a valve and driven by a first camshaft cam which includes a cam protrusion and a base circle, and a coupling lever driven by a second camshaft cam which includes a cam protrusion and a base circle. The levers are supported on a common lever pin so as to be pivotable relative to one another and can be connected together by a coupling apparatus comprising a first coupling element applied to one of the levers and a second adjustable coupling element applied to the other lever and acting in the coupled condition on the first coupling element, with the second coupling element being triggered for adjustment thereof.
DE 34 45 951 C2 describes a known actuator in which adjustment of the adjustable coupling element at an undesired time is prevented by an additional control lever which acts on the coupling apparatus. This apparatus is expensive, heavy, subject to wear, and requires additional installation space.
An object of the present invention is to provide an apparatus for valve actuation which prevents initiation of a coupling procedure or decoupling procedure at an undesired time or period, without additional weight and installation space occurring or considerable complication having to be incurred.
This object has been achieved in an apparatus in accordance with the present invention by providing that the adjustable coupling elements are triggered within a setting range of the camshaft which is predetermined so that the coupling elements of each coupling apparatus have at least a predetermined limiting overlap or are completely decoupled at a time when a cam protrusion associated with the coupling apparatus becomes effective.
In the apparatus according to the present invention, the common triggering of all the coupling apparatuses within a narrowly limited setting range of the camshaft reliably prevents the coupling apparatus associated with a cam protrusion from carrying out only a small part of the coupling procedure or from having substantially completed the decoupling procedure at the time when the cam protrusion becomes effective. Because the coupling apparatus is subject to considerable forces when the associated cam protrusion subsequently becomes effective, which forces prevent completion of the coupling or decoupling procedure, edge pressures and excessive surface contact pressures can occur in this coupling condition with little overlap between the coupling elements. This leads to wear and damage to the coupling elements or, if the coupling is cancelled under load, to the levers and cams.
The apparatus of the present invention ensures that mutually independent coupling conditions with unfavorably slight overlap of the coupling elements are avoided during both the coupling procedure and the decoupling procedure.
According to one embodiment of the coupling apparatus, a dimension for the overlap of the coupling elements which reliably prevents, on one hand, excessive loading on the coupling elements or the ejection of the movable coupling element and, on the other hand, limits the undesired period for the beginning of a coupling procedure such that sufficient time remains to ensure that the coupling procedure begins outside the undesired period even in the case of a multi-cylinder internal combustion engine and the higher rotational speeds of this internal combustion engine which are decisive for the coupling.
A type of triggering of the adjustable coupling elements which can be carried out by the present invention in a simple manner and permits the expectation of adequate timing accuracy. This is made more precise by another aspect of the present invention in which the duration of the triggering range of the coupling elements is determined exclusively by the switching time variance of the switching valve, whereas the triggering of the switching valve can be fixed by the use of an electrical signal at a certain time, i.e. practically without triggering time variance.
The configuration of the valve actuator of the apparatus in accordance with the present invention takes account of different coupling speeds of the adjustable coupling element during the coupling procedure due to different viscosities, and therefore flow speeds, of the hydraulic medium due to different temperatures so that the limiting overlap is reliably achieved within the desired times even under these changed boundary conditions.
The configuration of the apparatus in accordance with the present invention also permits the periods permissible for the triggering of the coupling apparatus in the case of multi-cylinder internal combustion engines to be extended or, if these periods remain unchanged, the configuration makes it possible to increase the rotational speed of the internal combustion engine which is decisive for a coupling procedure.